How can I see what file system mount is using when I use the "-t auto" flag?

I am using a minimal build of Yocto Linux so I cannot simply use "file" to see what it is after the fact.

  • Do you have the usual df command? The -T option includes a column for filesystem type. If not, you'll want to extract it from /proc/mounts. – Toby Speight Jun 29 '17 at 16:32
  • My version of BusyBox only gives Pkmh for df, no -T option – ClydeTheGhost Jun 29 '17 at 16:48

The filesystem type is the third column in /proc/mounts; to extract that column, you can write:

awk '{print $3}' /proc/mounts

To make it more specific, you need to match the second column with your mountpoint:

awk "\$2 == \"$mountpoint\" {print \$3}" /proc/mounts

man mount gives a verbose description of that case:

If no -t option is given, or if the auto type is specified, mount will try to guess the desired type. Mount uses the blkid library for guessing the filesystem type; if that does not turn up anything that looks familiar, mount will try to read the file /etc/filesystems, or, if that does not exist, /proc/filesystems. All of the filesystem types listed there will be tried, except for those that are labeled "nodev" (e.g., devpts, proc and nfs). If /etc/filesystems ends in a line with a single *, mount will read /proc/filesystems afterwards. While trying, all filesystem types will be mounted with the mount option silent.

  • My question was more directed at, once it finds a filesystem that works (i.e. it guesses correctly), is there a command to show which one it picked? – ClydeTheGhost Jun 29 '17 at 15:50

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